Finishing varnish for application over lithographic ink



Patented May 27, 1952 UNITED star FINISHING VARN'ISiH FOR APPLICATION OVER LITHOGRAPHIC INK Paul W. Greubel, Great Neck, N. Y., assignor to American Can Company, New York, N. Y., a corporation of New Jersey No Drawing.

Application April 8, 1948,

Serial No. 19,876

1 The present invention relates generally to finishing varnishes for lithographic inks and more particularly to novel improvements in those finishing varnishes which are applied over wet lithographic inks printed upon various web or sheet materials especially sheet metal, such as tin plate, terne plate, enameled sheet metal, etc. and to methods of varnishing over wet lithographic ink, in which the methods the ink pigment is fiocculated upon application of the varnish, thereby preventing bleeding and ridging of the ink.

- For many years it has been the practice, for example, in the decorated or lithographed sheet metal container art, to pass freshly lithographed metal sheets thru ovens for the purpose of dry ing the lithographic ink printed thereon before applying the finishing varnish which constitutes the final coating operation. Finishing varnishes are used to protect the lithographed surface and to improve its appearance by producing a'hard, protective and glossy finish.

Later, attempts were made to economize these operations by applying the wet finishing varnish directly over the wet ink and then passing the web or sheet thus coated thru the drying oven, thus drying both the wet ink and the Wet varnish coats in a single operation. This process .is known in the art as wet varnishing or wet ink varnishing. It saves considerable time and labor and would have many advantages if it were com pletely successful. However, the results obtained are unpredictable and have been far from satisfactorily uniform. It has been partially successful with only a relatively few finishing varnish formulations. In addition to restricting the use of many desirable and commercially required varnish formulations, the main difficulty has been inferior appearance such as lack of sharpness and lack of gloss in the finished lithographed product. 'More specifically, the inferior appear ance is due to the bleeding or running of the ink under the leveling action of the varnish coating, the ink flowing away from the printed areas at the edges; also the ink flows into macroscopic ridges or Waves in the more solid areas thereby producing a mottled and/or raised effect.

After extensive observations, experiments and tests conducted over a considerable period of time, I discovered the causes or reasons for those undesirable results. I found that they are due to certain physico-chemical phenomena similar to those which occur in the process of detergency. By experimenting with a great many different varnishesand inks, applying each varnish over a 22 Claims. (Cl. 26033.2)

given ink and conversely applying a given varnish over each of a series of different inks and also mixing the respective inks and varnishes and observing them microscopically I found that in all cases of failures there occurred a local movement of the ink film similar in action to that of detergency or washing away and that the pigment particles of the ink film were always defiocculated. Close examination revealed that the two undesirable phenomena, 1. e. bleeding or running and ridging or waving are the same in principle, each being the result of a disturbance or movement of the ink as leveling of the finishing varnish occurs. I also found that in all cases where bleeding and ridging did not occur, the pigment was always flocculated and Where these undesirable phenomena did occur the pigment was always 1 a state of clefiocculation.

Upon discovering the reason or cause of the trouble, 1. e. deflocculation of the ink pigment, I started the search for a proper remedy. It occurred to me that the di-ficulties could probably be overcome by searching out and utilizing lithographic inks and finishing varnishes which are completely or at least substantially immiscible. I soon discovered that this approach to the solution of the problem Was impractical in view of the present state of the art. The film forming materials used in both inks and varnishes are usually essentially of the same general nature, i. e. both may be made-from drying oils with or without resins or the finishing varnish usually contains a solvent which is also a solvent for the ink vehicle. Therefore, this method of approach would be successful only with very few and very carefully selected materials. This would severely limit the choice of materials from which the inks and finishing varnishes could be made. Since commercial requirements make it imperative to have as wide a range of materials available as possible for use in this process, I searched for. other means of solving the problem.

Next I thought of producing a flocculated ink by incorporating a flocculating agent in the ink during its manufacture. This method also proved impractical because an ink strongly flocculated before printing possesses certain undesirable characteristics which make it difficult to handle in the printing presses.

I then discovered that all the desirable results from a commercial use standpoint can be best secured by the incorporation of a flocculating agent or a combination of fiocculants in a finishing varnish which on contact with the wet lithographic ink positively induces a strongly 3 flocculated structure in the ink pigment and prevents bleeding or ridging of the ink when the varnish is applied over the wet ink.

Water and certain water soluble organic substances are known to induce flocculation in systems of solids in organic vehicle's. Starting with this general knowledge I experimented with a great number of likely materials to test their suitability for my specific purpose. I discovered that while such flocculating materials come from various chemical classes or groups the-suitable and successful ones, irrespective of their varying chemical composition, ultimately'group -them= selves under a common class-whichcan be'defined by their common physical characteristics. They must all be liquids. They T must :allbe substantially immiscible or at least of a very .low order of miscibility with the ink vehicle-finishing varnish system. The term immiscible is used in a relative sense. They must all have certain polar behavior.

Polar compounds are those in'which'the force uniting the atoms in the chemical bond is the electrostatic attraction'between oppositely charged particles. This electrostatic attraction ispresent in ionizable compounds and in compounds having electrostatic dissymmetry or oppositely-charged groups in their spatial structure.

Immiscible liquids are those wherein one liquid will'not blender dissolve in-another or willblend ordissolve only to a very limited degree, such that whenthey are poured together two distinct or-separate layers or phases result. Absolute immiscibility may be said to be non-existent and may be assumed to "be useless =as'a fiocculant 'since'this would imply absolute immiscibility with the other liquids in the wet 'varn'ish system. Immiscible in connection with "the'present inventionrefers to-a relatively low order of miscibilityin the ink vehicle-finishing varnish system. The forceof flocculation induced by immiscible liquids decreasesas miscibility increases.

And finally these materials must be incorporated'in the finishing varnish in certain percentages by weight, which vary with different varnish compositions and ink compositions, which percentages will beeifective in inducing immediate flocculation of thepigment inthe lithographic ink.

While immiscibility' or substantial immiscibility of the 'flocculating liquids is a necessary characteristicI discovered that because of the low order 'of miscibility of these compounds this desirablecharacteristic is accompanied by the phenomenon ofsometimes establishing a two-phase system in the finishing varnish. Therefore it is sometimes necessary that the immiscible flocculant be rendered sufficiently accessible to the lithographic pigment so that'it can come into intimate contact with said pigment whereby it increases the interfacial tension between the pigment surface and ink vehicle, which will'result in immediate, strong flocculation of the lithographic ink pigment. Isolved this problem by introducing'a coupli'ng'agent or mutual solvent into the varnish composition. The coupling agent or mutual solvent must be miscible with the ink vehicle, the varnish vehicle and the 'fiocculant. The'functi'on'of the'coupling' agent or mutual solvent is to maintain the varnish-fiocculant'mixfurther to continue'to maintain'a single liquid phase when such mixture is applied to the wet ink so that the flocculant can readily penetrate the ink vehicle in order to gain access to the ink pigment. Where a certain solvent already in the varnish composition is capable of functioning as a coupling agent, no additional or a lesser amount of coupling agentis required.-

Amongthe vfloccnlants which .I have found to be satisfactory are:

(1) Water (2) .Alkanols toffrom one to three carbon atoms inclusive such as methanol, ethanol, isopropanol, normal propanol (8) .Lactic. acid (commercial U. S. P. grade) (4) .Formamide (5) Dihydric alcohols of from two to four carbon atoms inclusive, such as: Ethylene glycol, propylene glycol, trimethylene glycol, diethylene glycol, etc.

(6) Glycerol For the purpose 'oflthe present invention I prefer to emphasizeethylene-glycol;

All of the'flocculants'which I foundto be satisfactory including those specifically mentioned come under the definition relatively'oil immiscible, water solublepolar liquids. The wordoilin this definition, for the purpose. of my invention, means thewater' insoluble oil,resin oriother film forming tmaterials constituting the vehicle of lithographic. inks. My extensive experiments and'tests conclusively show that no materialor compound which does not come under this definition. iunctions .asasatisfactory flocculant and conversely all materials oncompounds which. do

' answer this definition are -,good' fiocculants.

Ethylene glycol falls under the-classification of relatively oil immiscible water soluble polar liquids.;.

.Ethyleneaglycol, with .or without coupling agents; is incorporated 'intofthe finishing varnish formulation,.in-such percentages .by-weight of complete finishing varnish as will-result in-the requiredor optimum. flocculation in. the wet ink film.

.The percentage 1.01 fiocculant required varies .in-"accordance rwith the particular varnish: com

po'sitiontmxwhich' it :is. to be :embodied. It "varies in accordance with the flocculating force or ability of the :particular .rfiocculant itself, 'And it imay vary in accordance with the particular lithographic"inkjpigment which it is :to fluoc culate. For example, I have found that Milori blueirequires a :higher percentage of: 'fluocculant than. :any other lithographic ink 1 pigment, and that whenbleeding, andridging of this .pigment is stopped, bleeding-and ridging of all other pigments also is-controlled.

The required percentage of fiocculant in each commercialformulation of: finishing varnish for stopping either:bleeding or ridging can be reaching progressively increasing amounts of flocculating agent or mixture of flocculants, and

coupling agent when necessary, to the remainder. A particular ink 'is'rolled onto :a'strip of white enameled 'metal"-plate,' leaving a sharp, white uninked margin. One'strip'of wet-inked plate is dipped (white margin down) into'each varnish-flocculating agent mixture, and then 'allowed to drain. Bleeding, if present, will readily be observed against the background or the white with the procedure described under bleeding.

However, instead of dipping the strip of wetinked metal plate into the varnish, the varnish is applied over the wet ink by means of a roller.

The plate remains fiat at all times during this procedure. Ridging, if it occurs, can best be observed by looking at the ink from a 90 degree angle. I have found that ethylene glycol is very effective in percentages of from about 2 to 14 per cent, but the practical range (which may be considered the critical range) is wider and extends from about 1.0 per cent to 17 per cent, depending upon'the varying factors heretofore mentioned. Where a coupling agent or mutual solvent is required, I found that the most satisfactory compounds are those which have a group that is water-like in character or which may be said to impart water soluble characteristics. The most desirable coupling agents all have a free organic hydroxyl or alcohol group or an acetylated alcohol group and all come under the classifications of aliphatic alcohols and glycol monoethers or acetates of the glycol monoethers. They may be graphically represented by R(O) R in which R is a straight chain aliphatic carbon chain of four (4) to eight (8) carbon atoms or a glycol monoether in which both the glycol and ether n portions of the molecule have from two (2) to four (4) carbon atoms, and R. is a hydrogen atom or an acetate radical.

The following are suitable as coupling agents either singly or in combination for all my purposes:

The film forming materials from which metal decorating finishing varnishes are generally prepared and with which the principles of the present invention may be successfully employed include:

A. Polyester polymers ALKYD RESINS Alkyd resins formed by the reaction of polyhydric alcohols and polybasic carboxylic acids and their anhydrides, modified with non-drying, semi-drying or drying oils, with or without rosin, with or without mono or poly-functional phenolic bodies.

1 71.0% Soya modified alkyd resin solution 50% v solids (film former) V 5.7 Ethylene glycol (fiocculant) 23.3% Diethylene glycol monobutyl ether (cou pling agent) 2 58.8% Phenol modified alkyd resin solution 50% solids (film former) 6 9.4% Ethylene glycol (flocculant) Y r 31.8% Diethylene glycol monobutyl ether (coupling agent) B. Polyethers of polyhydrory compounds. ALLYL ETHERS OF POLYHYDROXY COMPOUNDS 1 34.7% Allyl starch (solid) (film former) 30. Toluene (resin solvent) 13.8% Ethylene glycol (fiuocculant) 21.3% Diethylene glycol monobutyl ether (coupling agent) C. Condensation polymers of aldehydes arid amines or alcohols ALKYLATED REACTION PRODUCTS OF AMINES,

SUCH AS UREA OR MELAMINE AND AN ALDE- HYDE, SUCH AS FORMALDEHYDE 83.3 Urea melamine aldehyde resin solution 50% solids (film former) 10.0% Ethylene glycol (fiocculant) 6.7% Diethylene glycol monobutyl ether (coupling agent) Oondensation polymer of a polyvinyl alcohol and aldehyde POLYVINYL-BUTYRAL 6.5% polyvinyl butyral (solid) (film former) 41.6% Butanol (resin solvent) 7.4% Ethylene glycol (flocculant) 44.5% Ethylene glycol monobutyl ether (coupling agent) 1). Vinyl halide-oinyl ester copolymers VINYL CHLORIDELVINYL ACETATE 16.0% Vinyl chloride-vinyl acetate copolymer (solid) (film former) 28.0% Methyl isobutyl ketone 24.0% Xylene 12.0% Isophorone 6.4% Ethylene glycol (flocculant) 13.6% Diethylene glycol monobutyl ether (coupling agent) E. Rosin modified oleoresinoas varnish 77.4% Rosin modified oleoresinous varnish solution 70% solids (film former) 3.1 Ethylene glycol (flocculant) 19.5% Diethylene glycol monobutyl ether (coupling agent) The formulae cited are typical examples of my invention. Many more could be added.v

A lubricant may be added to the finishing varnish if the sheet metal is to be subjected to fabricating processes after lithographing. The

Resin solvents addition of a lubricant (which is optional) will,

of course, vary the indicated percentages of ingredients to a slight degree. customarily, the lubricant is added in the form of a solution and the amount iss-regulated Shtfifllilith ubricant solids arerequivalentszto approxim tely iltmm per "film formers mayibeused singly, or in any compatible combination, depending on the film char- .zjcteristi s desired iAnyo-nezskille'cl in theart of varnish makings willi'bel ablej toprepare the various varnishes which may be used in connection with my disclosed invention.

The ;above examples arefor the purposev of illustrating the essential spirit of the present; invention, that is to say, the finishing ivarnish is formulated in :such a manner as to -enable the same to induce a fiocculated structure in the lithographic ink.

My extensive experiments conclusively indicate that the finishingvarnishes covered by the invention hereinbefore described may be applied over any and all wet lithographic inks composed of organic and/or inorganic pigments dispersed in a drying oil and/or resin modified drying oil and/or other ink vehicles such as ordinarily used. in-lithography, especially metal lithography.

It is thought that the invention andmany of its attendant advantages will be understood from of an:v organic solvent soluble resinouscondensation product f an amineand an aldehyde as a film forming ingredient, and a volatile organic solvent mixture for said ingredient, said mixture being misciblewith the ink vehicle and-containing from 1 to 17% by weight based on the finished varnish of ethylene glycol as ,an ink pigment flocculatingpagent and sufficient coupling agent selected from the group consisting of unsubstituted monohydric alkanols having from -4 to,,8 carbon atoms and glycol monoethers having from 2 to 4 carbon atoms in the glycol portion oi -the molecule and having .one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon .substituent having from 2 to 4 carbon atoms to maintain the ingredients in'a single liquid phase.

2. A finishing varnish for application over wet lithographic ink, said finishing varnish consisting of tan organic solvent/soluble synthetic resin .and-organicacid vinyl esters, as film forming ingredients, and .a volatile organic solvent mixturefor said ingredients, said mixture being mis- ..ciblelwith the ink .vehicle and containing, from vltol'l %x-.-by weight based-on the finished varnish :8 ofzethvleneelvco geese. inheisment;fleeeulatins agent and sufiicient unsubstituted monohydigic alkanol having from-4. to 8 carbon atoms to maintain the ingredients ina single liquidphase.

3: Afinishirrg varnish ffD! application over-wet lithographic ink, said finishing varnish consisting of an organic solvent soluble synthetic resin selectedf'rom the group consisting-of alkyd resins, resinous polyethers of polyhydrosycompounds, condensation polymersof amineszand aldehyd'es, condensation polymers ,of aldehydes and polyvinyl alcohol, and copolymers of' vinylhali des and organic acid vinyl ,esters, asfilm forming n red ents. a o ati rgan c. solvent mixture for said ingredients; said mixture being mlscible with the ink vehicle and oontaininsirom Ito 1. by wei ht b se on h iinis ed v 0f t v sly ol as arism nflfiqcculiig and :sufiicient glycol 'monoether. ihaving. f

to '4 carbo ms. in the glyc j ortionrof. e

molecule and having one free hydroxyl. group and the other hydroxyl group etherifled'yvith an aliphatic hydrocarbon substituent hayin to 4 carbon 'atoms'to maintain the in a single liquid phase.

4. A finishing .varnish for application over wet lithograp c i sa d fi shina arnish c nsistin of an organic solvent soluble synthetic resin selectedfrom. thegroup consisting of alkyd resins. resinous poly ethers of pqlyhydroxy comnfll-lmi condensation polymers, of amines, and aldehydes, condensation polymers ,of aldehydes and, polyvinyl alcohol and. copolyrners oivinyl halides and organic acid vinyl esters ,as ,film .f o rming ingredients, and a volatile organic solvent mixturef r said in edi n asa d. m x u bein miscible with t e ink veh cle. and conta in item 1 to 17% by weight based on the finishedyernish of ethylene glycol as. an ink pigment, fiocculating a ent, and sufficient couplin a ent eIQQ Bdjirom the group consisting of unsubstituted monuhydrie alkanols having from 4 to 8 carbon atoms and glycol monoethers having-from 2 :to :4-carboi1 atoms in the glycol portion of. .the molecule :and having one free hydroxylxgroup and: the other hydroxyl group etherified-with an: aliphatic my:- drocarbon substituent having from 2 to 4::carbon atoms to maintain the. ingredients ina. single liquid phase.

5. A method of varnishing over wet lithographic ink, comprising, printing :a pigmented lithographic ink on asheetof :web materialand fiocoulating the inkpigmentby applying ;over he. wet inka fin shing varnish th t s uhstentially miscible with the ink vehicle and which contains an organic solvent soluble film forming resin in solution in a volatile organic-solvent, suflicient oil immiscible-Water soluble pigment flocculating agent selected from the group consisting of unsubstituted 'monohydric alkanols having froml to 3 carbon atoms ,andgl-ycols having from,,.2.,to 4 carbon atomsto efiect -rapid 9 formed by polymerization of a compound containing a vinyl group.

8. The method of claim 6 in which the resin is selected from the group consisting of alkyd resins, resinous polyethers of polyhydroxy compounds, condensation polymers of amines and aldehydes, condensation polymers of aldehydes and polyvinyl alcohol, and copolymers of vinyl halides and organic acid vinyl esters.

9. The method of claim 8 in which the resin is an alkyd resin.

10. The method of claim 8 in which the resin is a condensate of an amine and an aldehyde.

11. The method of claim 8 in which the resin is a resinous polyether of a polyhydroxy compound.

12. The method of claim 7 in which the resin is a copolymer of a vinyl halide and vinyl acetate.

13. The method of claim in which the web material is a metal sheet.

14. The method of claim 13 in which the metal sheet is tin plate.

15. The method of claim 13 in which the metal sheet is steel.

16. The method of claim 5 in which the flocculating agent is ethylene glycol in concentrations of 1 to 17% by weight of the finished varnish.

17. The method of claim 5 in which the coupling agent is an unsubstituted monohydric alkanol having from 4 to 8 carbon atoms.

18. The method of claim 5 in which the coupling agent is a glycol monoether having from 2 to 4 carbon atoms'in the glycol portion of the molecule and having one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon substituent having from 2 to 4 carbon atoms.

19. A finishing varnish for application over wet lithographic ink, said finishing varnish consisting of an alkyd resin as a film forming ingredient and a volatile organic solvent mixture for said resin, said mixture being miscible with the ink vehicle and containing from 1 to 17% by weight based on the finished varnish of ethylene glycol as an ink pigment flocculating agent and sufiicient coupling agent selected from the group consisting of "unsubstituted monoalkanols having from 4 to 8 carbon atoms and glycol monoethers in which the glycol portion of the molecule has from 2 to 4 carbon atoms and one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon substituent having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

20. A finishing varnish for application over wet lithographic ink, said finishing varnish consisting of an organic solvent soluble resinous polyether of a polyhydroxy compound as a film forming ingredient, and a volatile organic solvent mixture for said ingredient, said mixture being miscible with the ink vehicle and containing from 1 to 1'7 by weight based on the finished varnish of ethylene glycol as an ink pigment flocculating agent and sufiicient coupling agent selected from the class consisting of unsubstituted monoalkanols having from 4 to 8 carbon atoms and glycol monoethers in which the glycol portion of the molecule has from 2 to 4 carbon atoms and one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hy drocarbon substituent having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

21. A finishing varnish for application over wet lithographic ink, said varnish consisting of an organic solvent soluble resinous copolymer of a vinyl halide and an organic acid vinyl ester as a film forming ingredient and a volatile organic solvent mixture for said ingredient, said mixture being miscible with the ink vehicle and containing from 1 to 17% by weight based on the finished varnish of ethylene glycol as an ink pigment flocculating agent and suflicient coupling agent selected from the group consisting of unsubstituted monoalkanols having from 4 to 8 carbon atoms and glycol monoethers in which the glycol portion of the molecule has from 2 to 4 carbon atoms and one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon substituent having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

22. A finishing varnish for application over wet lithographic ink, said varnish consisting of an organic solvent soluble alkydresin admixed with a drying oil as a film forming ingredient and a volatile organic solvent mixture for said ingredient, said mixture being miscible with the ink vehicle and containing from 1 to 17% by Weight based on the finished varnish of ethylene glycol as an ink pigment flocculating agent and sufiicient coupling agent selected from the group consisting of unsubstituted monoalkanols having from 4 to 8 carbon atoms and glycol monoethers in which the glycol portion of the molecule has from 2 to 4 carbon atoms and one free hydroxyl group and the other hydroxyl group etherified with an aliphatic hydrocarbon substituent having from 2 to 4 carbon atoms, to maintain the ingredients in a single liquid phase.

PAUL W. GREU'BEL.

REFERENGES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. A FINISHING VARNISH FOR APPLICATION OVER WET LITHOGRAPHIC INK, SAID FINISHING VARNISH CONSISTING OF AN ORGANIC SOLVENT SOLUBLE CONDENSATION PRODUCT OF AN AMINE AND AN ALDEHYDE AS A FILM FORMING INGREDIENT, AND A VOLATILE ORGANIC SOLVENT MIXTURE FOR SAID INGREDIENT, SAID MIXTURE BEING MISCIBLE WITH THE INK VEHICLE AND CONTAINING FROM 1 TO 17% BY WEIGHT BASED ON THE FINISHED VARNISH OF ETHYLENE GLYCOL AS AN INK PIGMENT FLOCCULATING AGENT AND SUFFICIENT COUPLING AGENT SELECTED FROM THE GROUP CONSISTING OF UNSUBSTITUTED MONOHYDRIC ALKANOLS HAVING FROM 4 TO 8 CARBON ATOMS AND GLYCOL MONOETHERS HAVING FROM 2 TO 4 CARBON ATOMS IN THE GLYCOL PORTION OF THE MOLECULE AND HAVING ONE FREE HYDROXYL GROUP AND THE OTHER HYDROXYL GROUP ETHERIFIED WITH AN ALIPHATIC HYDROCARBON SUBSTITUENT HAVING FROM 2 TO 4 CARBON ATOMS TO MAINTAIN THE INGREDIENTS IN A SINGLE LIQUID PHASE. 